Applying interpolation within a convex hull

Hi there,

I have been using the Tps function (within the Fields package) for a while
now to interpolate different sedimentary units. Due to the method of
formation of the units I know that at some edges the thickness of the unit
decreases to zero. I was wondering if there was someway to specify that the
interpolation only occurs within the convex hull of the data, outside of
which the the values are zero. I am having problems with the output surface
'curling' up at distance from the data.

The interp() (and interpp()) functions in the "akima" package have
argument "extrap" which defaults to FALSE whence interpolation
is confined to the convex hull of the data.  Sounds like what you
want.

     cheers,

         Rolf

Thank Rolf, 

I am aware of the extrapolation possibilities within the interpolation
packages within akima but this interpolation often leads to unrealistic
results for my sedimentary units. Therefore I would like to be able to just
apply the interpolation to the thickness measurements within the convex hull
of the data with the interpolation taking into account that everywhere
outside of the convex hull the thickness value is zero rather than
increasing again. I would specifically like to apply this to the Tps
function as using this function I can apply weights to my data which I can't
in the akima fucntions. 

Thanks again, 
Sam

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